A magnetometer is a sensor capable of measuring magnetic flux density on one or more vectors (axes). Some mobile communications devices use embedded magnetometers to measure the Earth's magnetic field strength to provide, among other things, compass bearings. However, embedded magnetometers are subject to interference from what are commonly referred to as “hard iron” offsets and “soft iron” distortions. Hard iron offsets are created by objects that produce a magnetic field, for example, a permanent magnet in the speaker of a mobile communications device. Soft iron distortions are deflections or alterations in the magnetic field produced by ferromagnetic materials that, while they do not produce a magnetic field themselves, influence the magnetic field being measured. In a mobile communications device, such materials include, for example, metal shielding, metal fasteners, antennas, batteries, and conductors.
Because hard iron offsets are constant regardless of orientation, the values of the offsets may be determined with an accelerometer during movement of the mobile communications device. The mobile communications device may be configured to compensate for the hard iron offsets by subtracting the values from magnetometer measurements to arrive at calibrated magnetic field flux density readings. However, soft iron distortions vary with orientation, and therefore cannot be precisely determined using accelerometer readings alone. In addition, soft iron distortion effects vary with the operation of the mobile communications device.
Accordingly, there is a need for systems and methods for magnetic interference compensation of an embedded magnetometer.
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